Ask the Master Gardeners: How to banish black spot?

Jul. 18, 2008

Q: Every June my roses look beautiful. A month later they're scrawny and covered in black spot. Short of using a fungicide, is there a preventive solution?

A: The best defense is a strong offense. There are a number of ways to decrease the odds of your roses developing black spot.

The first is to plant disease-resistant varieties. Any rose recently selected as an "All-America" winner will be highly disease-resistant because that is one of the most important criteria in the selection process.

Once you have selected your roses, take care to plant them in the right spot. They need well-drained soil and good air circulation to flourish. Proper air circulation is vital to the health of your plants.

Correct watering technique is also key to disease prevention. Water at the base and try to keep the leaves from getting wet.

Be vigilant - monitor your roses carefully and at the first sign of black spot remove any affected leaves.

Also clean up any leaves or spent blooms that have fallen from the plant. You will notice that when black spot develops, it moves up the plant from the bottom.

If you follow these guidelines and still find black spot out of control, you will need to start a spraying program using a fungicide approved for roses. Your county Cornell Cooperative Extension office will have the specific information you need.